Hyaluronic acid is a nonsulfated glycosaminoglycan, linear polysaccharide with a very large molecular weight of 200,000 to 400,000 composed of repeating glucuronic acid and N-acetylglucosamine residues. Hyaluronic acid is a major structural component of the extracellular matrix and involved in water retention, maintenance of the extracellular space and storage and diffusion of cell growth factors and nutrients, as well as in cell proliferation and differentiation, and migration.
In mammals, it has been reported that 50% or more of their hyaluronic acid exists in the skin, particularly in epidermal extracellular space and dermal connective tissue, and it is synthesized by keratinocyte and fibroblasts. Further, the concentration of hyaluronic acid in human skin decreases with aging, which causes the skin to lose its elasticity and to decrease water retention (Biochem Biophys Acta 279, 265-275, Carbohydr Res 159, 127-136, Int J Dermatol 33, 119-122).
The human joint capsule is composed of the outer fibrous layer and the inner synovial membrane, in which synovial fluid containing hyaluronic acid and glycoprotein, functions as a joint lubricant. It has however been reported that in osteoarthritis (degenerative arthritis), the production of hyaluronic acid decreases and destruction by proteolytic enzymes is accelerated, so diminishing the concentration of hyaluronic acid in a joint. Therefore as the concentration of hyaluronic acid in a joint decreases, the joint cannot absorb or disperse shocks, so accelerating cartilage damage. Hence, hyaluronate injection was approved by the FDA in 1997 as a device for the relief of pain from osteoarthritis and has been applied thereto. However, in the end, it may be more effective to increase the biosynthesis of hyaluronic acid.
The biosynthesis of hyaluronic acid in cultured epidermal cells has been reported to be increased by various growth factors and by trans-retinoic acid, N-methylserine and the like (Biochem. J. 258, 919-922, Biochem. J. 283, 165-170, Biochem. J 307 817-821, J. Biol. Chem. 272,4787-4794, J Invest Dermatol 92, 326-332, Biol Pharm Bull 17, 361-364, Skin Pharmacol Appl Skin Physiol 12, 276-283). Further, there were reports that estradiol and its derivatives applied on the skin might increase the biosynthesis of hyaluronic acid (Steroids 16,1-3, J Invest Dermatol 87, 668-673, Skin Pharmacol Appl Skin Physiol 15, 175-183). However, the detailed mechanism for the metabolism of hyaluronic acid has not yet been fully elucidated. It has been merely known that hyaluronic acid is synthesized at the inner surface of the plasma membrane by hyaluronic acid synthase and is extruded through the membrane into the extracellular space simultaneously with the ongoing synthesis (J. Biol. Chem. 272, 13997-14000).
Currently, three different HAS genes have been identified in mammalian cells: HAS1, HAS2 and HAS3 which are highly homologous. In relation thereto, it was reported that HAS2 gene expression increased when an epidermal growth factor (EGF) was contained in a medium of epidermal cell line culture (J. Biol. Chem. 276, 20428-20435). However, studies on distribution of hyaluronic acid in cells and tissues and on various factors and enzymes related to hyaluronic acid, for example HAS or factors regulating the activity of hyaluronic acid, remain insufficient up to now.
Therefore, several continuing studies have paid attentions to the possibility of hyaluronic acid, and have extensively researched to find effective production and injection of hyaluronic acid and methods for increasing the biosynthesis of hyaluronic acid. However, obvious results are not yet known.